So far methods of improving grip performance on ice and snow of tires for use in winter such as a studless tire and a snow tire have been proposed, for example, a method of increasing adhesive friction force by decreasing a hardness (Hs) of a rubber composition for a tread, thereby decreasing an elastic modulus at low temperature (improving low temperature property), a method of obtaining a gripping force on an ice- and snow-covered road by providing predetermined sipes on a block surface of a tread, and a method of obtaining a gripping force by providing, on a tread surface, deep lateral grooves for compressing snow and gripping the compressed snow during running.
The sipes provided on a block surface of a tread come into contact with ice and snow on a road, thereby making it possible to exhibit a gripping force. However, when “sticking of snow”, which is a phenomenon of snow adhering to a surface of a tread, occurs, there is a problem that the sipes cannot come into contact with snow and ice on a road, thereby making it impossible to exhibit grip performance on ice and snow.
Snow gripped by the lateral grooves is removed until a tire makes one rotation and the lateral grooves come into contact with snow on the road again. Thus, the lateral grooves can exhibit the gripping force repeatedly. However, when “clogging of snow” occurs and snow cannot be removed from the tread, there is a problem that the lateral grooves cannot grip snow, namely on-snow grip performance which the tire has cannot be exhibited.
In order to solve the above-mentioned problems, a method of forming a tread pattern such as lateral grooves into a predetermined shape has been proposed. For example, JP 2008-221955 A discloses a method of inhibiting sticking of snow by forming a tread pattern into a predetermined shape. Further JP 2014-080050 A discloses a method of inhibiting the clogging of snow by designing lateral grooves to have a predetermined shape.